1.1. Mitosis and meiosis are important in the life cycles of organisms.

Hydra is a small animal that lives in fresh water. When environmental conditions are favourable, Hydra reproduces asexually. Large numbers of offspring can be produced in this way.

Asexual reproduction in Hydra is shown in Fig. 19.1.

Fig. 19.1

(i) Asexual reproduction involves mitosis.

Name the stages of mitosis in the correct order.

 [2]

(ii) Suggest why Hydra reproduces asexually when conditions are favourable.

 [2]

1.2. When conditions are not favourable, Hydra reproduces sexually. This often happens in the winter.

Cells in the body wall produce sperms and eggs by meiosis.

Large numbers of sperms are released into the water. These sperms can fertilise eggs from different individuals. Each egg forms a tough outer coat, and can lie dormant at the bottom of the water until conditions improve.

(i) Explain how sexual reproduction in Hydra leads to genetic variation in the offspring.

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(ii) Suggest why sexual reproduction in Hydra usually occurs in the winter.

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1.3. Mosses are small plants that live in damp conditions.

The life cycle of many mosses involves two stages: a gametophyte and a sporophyte.

The gametophyte contains haploid cells and produces sperms and eggs.

The sporophyte contains diploid cells and produces spores which can be spread easily through the air.

The spores germinate and grow into a gametophyte.

Fig. 19.2 shows the life cycle of the moss Funaria.

Fig. 19.2

(i) The zygote grows into the sporophyte by mitosis.

The haploid gametophyte of one species of Funaria contains 28 chromosomes.

A single DNA molecule contains two strands.

Calculate the number of strands of DNA present in the nucleus of the zygote immediately before mitosis.

[1]

(ii) Mark an X on Fig. 19.2 at the point at which meiosis occurs.

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(iii) A diagram of a moss sperm is shown in Fig. 19.3.

Fig. 19.3

The flagella allow the sperm to move towards an egg.

Suggest and explain another adaptation that is likely to be present in these sperm cells.

[2]